Transmission of moving pictures in real-time is employed in several applications like e.g. video conferencing, net meetings and video telephony.
Video conferencing systems allow for simultaneous exchange of audio, video and data information among multiple conferencing sites. Systems known as Multipoint Control Units (MCUs) perform switching functions to allow the endpoints of multiple sites to intercommunicate in a conference. The MCU links the sites together by receiving frames of conference signals from the sites, processing the received signals, and retransmitting the processed signals to appropriate sites. The conference signals include audio, video, data and control information. In a switched conference, the video signal from one of the conference sites, typically that of the loudest speaker, is broadcast to each of the participants. In a continuous presence conference, video signals from two or more sites are spatially mixed to form a composite video signal for viewing by conference participants. When the different video streams have been mixed together into one single video stream, the composed video stream is transmitted to the different parties of the video conference, where each transmitted video stream preferably follows a set scheme indicating who will receive what video stream. In general, the different users prefer to receive different video streams. The continuous presence or composite video stream is a combined picture that may include live video streams, still images, menus or other visual images from participants in the conference.
Video conferencing between separated networks need also some kind of arrangements to traverse firewalls, because firewalls usually do not accept standardized communication sessions, such as session initiation protocol (SIP), H.323 and WebRTC, to cross a network edge e.g. the edge of an enterprise network. Such arrangements may include proxies outside and inside the enterprise network, making the communication between the proxies acceptable for the firewall.
FIG. 1 illustrates an example of a firewall traversal setup according to prior art. In this example, three video conferencing terminals participate in a conference call, and two nodes (e.g. MCUs) are facilitating the call. Terminal 1 and Terminal 2 connected to Conferencing Node A, are all located outside an enterprise firewall, and Terminal 3 as well as Node B, to which it is connected, are located behind the enterprise firewall. Node A is transcoding the mixed conference.
Terminal 3 connects to Conferencing Node B. Conferencing Node B hosts a transcoded and mixed MCU conference B, which is cascaded to the MCU conference on Conferencing Node A. In this case, standardized communication sessions as established between the terminals and the nodes, as well as between the nodes A and B crossing the firewall. Then certain firewall traversal arrangements must be present for the communication sessions to be accepted by the firewall. The communication topology is also fixed during a conference. This is a drawback and it will increase along with growing demand for real-time HD multimedia data traffic requiring a more fragmented and distributed multimedia data processing and bandwidth usage.